1. Field of the Invention
The present invention relates generally to disk drives and more particularly to a method, apparatus, and computer program product for canceling or minimizing disturbances in rotating disk storage systems.
2. Description of the Related Art
Disk drives are magnetic recording devices used for the storage of information. The information is recorded on concentric tracks on either surface of one or more magnetic recording disks. The disks are rotatably mounted to a spin motor and information is accessed by means of read/write heads that are mounted to actuator arms which are rotated by a voice coil motor. The voice coil motor is excited with a current to rotate the actuator and move the heads. The read/write heads must be accurately aligned with the storage tracks on the disk to ensure proper reading and writing of information.
To accurately write and read data, it is desirable to maintain the head on the center of the track. To assist in controlling the position of the head, each sector of the disk typically contains a number of servo bits accurately located relative to the centerline and/or reference line of the track. The signals produced by the servo bits are demodulated and used to obtain a Position Error Signal (PES). The PES is used to calculate a correction current that is applied to the voice coil motor to move the actuator arm and head over the track centerline or reference line of a track.
In disk drives, the term xe2x80x9crunoutxe2x80x9d is typically used to describe position error sources. These sources of disturbances increase the PES. The track runouts and external vibrations in disk storage systems are either repeatable or non-repeatable. When the frequencies of the external disturbances are synchronous to the disk rotation frequency, the disturbances are classified as repeatable. Otherwise, the disturbances are non-repeatable. Many techniques are widely used to identify and cancel repeatable runouts and external vibrations.
Non-repeatable disturbances are more difficult to identify and cancel because they typically involve changes/modulations in frequencies as well as amplitudes. Non-repeatable runouts are typically caused by defects in the bearing, spindle motor imperfections, noise, and servo loop response error.
One technique for handling non-repeatable runouts involves the use of a fixed compensator. A fixed compensator usually relies on high bandwidth to provide adequate attenuation in the frequency regime of the non-repeatable disturbance. This technique is typically expensive to implement due to the stringent design requirements placed on mechanical designs.
Disclosed herein is a method for moving a transducer across a surface of a disk in a rotating disk storage device, where the rotating disk storage device is subjected to a non-synchronous disturbance signal. In one embodiment, the method includes moving the transducer across the disk surface, computing a design position of the transducer, determining an actual position of the transducer, and generating a position error signal (PES) at a plurality of positions between a source track and a destination track. The PES is a function of the design position, the actual position, and the non-synchronous disturbance signal. The method further includes generating a disturbance correction signal, at the plurality of positions, that is a function of the PES, providing a corrected PES, at the plurality of positions, that is function of the PES and the disturbance correction signal, and varying the movement of the transducer in response to the corrected PES.
Other embodiments are disclosed and claimed herein.